The invention relates generally to solar collectors and, more specifically, to an evacuated tube collector having a plurality of collectors disposed in a staggered array on a dual passageway manifold.
The sophistication of solar collectors has increased dramatically during the last decade. Nonetheless, every configuration including air or water media and flat plate or tube collector designs exhibits performance anomalies that encourage further inventive efforts. In evacuated tube collectors, which utilize air as a heat recovery medium, one area of difficulty has been uniform distribution of the air to the collector elements. Aside from problems of service life associated with operation of the collector elements at elevated temperatures, non-uniform air distribution may seriously degrade the operating efficiency of the collector.
A common answer to non-uniform fluid distribution is to increase the operating pressure and, thus, pressure drop across elements of the system. In solar energy equipment which utilizes air as a heat recovery medium, an increase in system pressure can only be achieved with a concomitant increase in the consumption of energy by the air moving components. Viewed as a thermodynamic system, such an increased energy input into the solar collector may and typically will result in decreased overall thermal efficiency. Thus, this approach may be fraught with difficulties and must be analyzed carefully from a thermodynamic standpoint to determine its overall effect on the efficiency of the system.
This situation suggests that low system pressures and minimal pressure drops may have merit. One such system is disclosed in my previous issued, co-owned U.S. Pat. No. 4,016,860.
Another area of difficulty in solar collector design may be characterized as load matching. The size and cost of solar collectors militates against the purchase and installation of devices capable of supplying energy in excess of demand. Thus, from an installation and purchase standpoint, it is desirable to closely match the output of a solar collector to a load. Due to their novelty and the contemporary market, however, from a manufacturing standpoint, it is not feasible to provide a broad range of solar energy recovery equipment having small incremental differences in energy output. A modular approach is therefore suggested, but the prior art is limited to modular equipment in which flow distribution, flow rates and pressure drops, particularly in air medium equipment, are problematical.